+1 to the other replies here, I think it's very poor form to throw the engineers under the bus for not being curious. The most likely explanation is they were under insane time and resource constraints, especially in the games industry. They wrote something that worked, then were forced to move on to the other 5000 tasks in their backlog that had to get done before release. When you're already being told to crunch 80+ hour weeks for months or years at a time, you run out of gas.

I guess it's possible that the engineers who were talented enough to create this extremely impressive game in the first place somehow threw up their hands and said "guess it can never take less than 7 minutes to load, best we can do". But it seems much more likely that they were well aware, but never allowed by poor management to go back and fix it. The game was released and printing money, why bother. They're on to the next title.